How to choose sludge conditioner for sludge treatment ? PART TWO
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How to choose sludge conditioner for sludge treatment ? PART TWO

Views: 15     Author: Ryde Environment     Publish Time: 2019-05-22      Origin: Ryde Environment

Sludge conditioner is usually used to improve the efficiency and effectiveness of sludge treatment. Sludge conditioner is needed in sludge dewatering process of plate-and-frame type filter press, centrifuge, belt filter press, multi disc screw press and so on. 

CentrifugeBelt filter press-1Multi disc screw pressplate and frame type filter press

As mentioned in the previous article, variety characteristics of sludge conditioners, sludge properties and temperature are the factors that affects the effect of sludge conditioner.


So besides these three factors, are there any other factors that will affect the effect of sludge conditioners?

Yes, there are other factors.

PH value

The pH value of sludge determines the hydrolysate form of inorganic salt conditioner, and the effect of the same conditioner on sludge with different pH values is also different.

The hydrolysis of aluminium salts is greatly affected by the pH value, and the optimum pH value of the coagulation reaction is 5-7. When the pH value is greater than 8 or less than 4, it is difficult to form flocs, that is to say, the function of conditioning is lost.

However, the effect of pH value on the ferric salt conditioner is small. Whether the sludge is acidic or alkaline, the hydrolysate Fe(OH)3 flocs can be formed. The optimum pH value range is 6-11. Ferrite hydrolysates with high solubility can be oxidized into Fe(OH)3 flocs with low solubility in sludge with pH value of 8-10.

Therefore, when choosing inorganic salt conditioner, we should first consider the specific pH value of dewatered sludge. If the pH value deviates from the optimum range of its coagulation reaction, we can replace another conditioner. Otherwise, it is necessary to consider adding acid or alkali to adjust the pH value of sludge before sludge treatment. Normally, no such measures are taken. 

PH value also affects the conditioning effect of polyelectrolyte, and sludge pH value affects the ionization, charge status and molecular shape of conditioner molecules. The ionization degree of cationic polyelectrolyte in acidic sludge with low pH value is higher and the molecular shape tends to stretch, while in alkaline sludge with high pH value, the ionization degree is smaller and the molecular shape tends to curl.

Contrary to the properties of cationic polyelectrolyte, anionic polyelectrolyte has a smaller ionization degree in acidic sludge with low pH value, and its molecular shape tends to curl, while in alkaline sludge with high pH value, its ionization degree tends to be larger and its molecular shape tends to stretch. The situation of cationic and anionic polyelectrolytes is slightly different. At the isoelectric point, the whole molecule is neutral, and the positive and negative charges attract each other, so the molecule is tightly curled into clusters. On both sides of the isoelectric point, there will be an excess charge on the molecule, which tends to stretch due to mutual repulsion.


Concentration of sludge conditioner

The concentration of sludge conditioner not only affects the conditioning effect, but also affects the consumption of chemicals and the yield of mud cake, especially the organic polymer conditioner.

Generally speaking, the lower the concentration of organic macromolecule conditioner is, the less the consumption of the agent is, the better the conditioning effect is. This is because the lower the concentration of organic macromolecule conditioner is, the easier it is to mix evenly, the better the molecular chain stretches, the better the bridging and coagulation function is, and the better the conditioning effect is, of course. However, too high or too low preparation concentration will reduce the yield of mud cake.

The conditioning effect of inorganic macromolecule conditioner is almost not affected by the concentration of the formulation. Experience and related studies show that the concentration of organic macromolecule conditioner is between 0.05% and 0.1%, that of ferric chloride is 10%, and that of aluminium salt is between 4% and 5%.

Usually, Sludge Conditioner are in a solid state to facilitate transportation and sales. In use, it is necessary to dissolve the solid sludge conditioner into a certain concentration of viscous water solution.

The function of Polymer preparation unit is to make the powder or liquid sludge conditioner dissolve or dilute into sludge conditioner solution. It is usually divided into manual dosing device and the integrated of dosing device. The integrated of dosing device is fully automatic operating including automatic dosing, dissolving and feeding.


Addition order

When more than one conditioner is used, the order in which the conditioner is added will also affect the conditioning effect.

When iron salt and lime are used as conditioning agent, iron salt is usually added first, then lime is added. The floc formed by this method can be easily separated from water, and the total consumption of conditioning agent is also less.

When inorganic conditioning agent and organic macromolecule conditioning agent are combined to treat sludge, inorganic conditioning agent is added first, and then organic macromolecule conditioning agent is added. Generally, better conditioning effect can be obtained.


Mixed Reaction Conditions

In order to achieve good conditioning effect, it is necessary to mix sludge and conditioner completely and fully.

However, it is worth noting that when sludge reacts with conditioner to form flocs, they can never be destroyed again, because once the flocs are destroyed, it is difficult to restore to their original state.

Experience shows that only when the intensity and time of mixing reaction are within a certain range, can a better conditioning effect be achieved for a certain sludge, and the conditioning effect will decrease with the increase of residence time.

That is to say, after determining the time and intensity of conditioning through experiments, it must be strictly observed in practice. On the one hand, the mixing reaction time can not be prolonged or shortened at will. On the other hand, the conditioned sludge should be put into the dewaterer as soon as possible.


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